This invention relates generally to medical leads and more particularly to implantable cardiac leads.
In the context of implantable leads, and particularly in the context of implantable cardiac leads, there is often a need to remove a lead after it has been implanted in a patient's body for some period of time. In conjunction with lead removal, it is often necessary to apply traction to the lead, in order to pull it free from tissue adhering thereto. It has therefore been recognized for some time that a reinforcement of some type, extending along the lead body would be beneficial, in order to prevent breakage or partial disassembly of the lead during removal. For example, in U.S. Pat. No. 5,231,996 issued to Bardy et al., a variety of reinforcement mechanisms are disclosed, including cords, filaments, braids, and the like.
More recently, in the context of implantable cardiac leads, the use of cabled or stranded conductors in place of the previously more commonly employed coiled conductors has become more popular. These cabled or stranded conductors, such as disclosed in U.S. Pat. No. 5,584,873 issued to Shoberg et al., U.S. Pat. No. 5,760,341 issued to Laske et al. and U.S. Pat. No. 5,246.014 issued to Williams et al. inherently provide an increased tensile strength lead, at least along the segment between the point at which the stranded or cabled conductor is coupled to an electrode and the point at which the conductor is coupled to an electrical connector at the proximal end of the lead. While this new conductor inherently provides a lead of enhanced tensile strength, in most transvenous cardiac pacing leads employing cabled or stranded conductors, the conductor which extends to the distal-most portion of the lead is still a coiled conductor in order to permit passage of a stylet. This distal-most portion of the lead, particularly in the context of leads employing tines or other passive fixation mechanisms, is the portion of the lead to be most likely to be firmly embedded in fibrous tissue. It is therefore desirable that this portion of the lead in particular should be capable of withstanding high tensile forces without breakage.